The present invention relates to a fluid friction clutch.
A fluid friction clutch of a type similar to that of the present invention is described, for example, in Applicant's German Offenlegungsschrift No. 30 09 665. A clutch of this type transfers a torque force by means of the fluid friction of a viscous medium located in the working gaps of the clutch. The working gaps, which are located between the drive disk and the clutch housing, are provided both on the front and the rear side of the drive disk, and a valve opening for supplying the viscous medium which is present in front of the drive disk. However, in clutches of this design, conditions for the supply of the viscous medium to the front and the rear working gap are different, thus frequently resulting in the rear working gap being inadequately filled with the viscous medium or being filled in an uncontrolled manner. This leads to undesirable torque or rpm flunctuations, i.e., the control behavior of such a clutch is unsatisfactory, because no defined correlation or functional dependence exists between the output speed of the clutch and the temperature which functions as the control parameter.
In the clutch described in German Offenlegungsschrift No. 30 09 665, the drive disk includes a plurality of radially extending elongated holes arranged aroundthe periphery of the drive disk in the area of the working gap, which permit passage of the viscous medium from the front to the rear side of the drive disk. In other clutch configurations, for example, according to German Auslegeschrift No. 11 37 271, passage bore holes are provided in a radial arrangement on the drive disk within the working gap. In another configuration according to German Offenlegungsschrift No. 26 37 694, so-called pump grooves are provided to improve the circulation of the viscous medium, so that the rear working gap may be more adequately filled. Finally, another solution to the present problem is described in German Offenlegungsschrift No. 26 23 570, wherein, in addition to the valve opening in the partition wall, an overflow orifice is provided through which the viscous medium continuously flows into the work chamber. However, none of the measures mentioned above results in a satisfactory solution to the problem.
Finally, a fluid friction clutch with scoop filling control is known, by German Offenlegungsschrift No. 21 30 568, wherein the viscous medium passes from a control chamber into the work chamber through a plurality of radially and tangentially offset bores in a partition wall. The primary disk of this clutch also comprises a plurality of radially and tangentially offset transverse bores through which the viscous medium passes from the front side to the rear side of the disk. The filling and emptying of the work chamber is effected by means of a pure transverse flow through the same bores, since the work chamber and the control chamber act as communicating vessels. There is, therefore, no circulation through an inlet and an outlet orifice, resulting in different inflow and outflow conditions.